RESPIRATION IN SOUTHERN WHALES 37i 



A whale at loo m. is subjected to an absolute pressure of ii atmospheres (1541b. per 

 sq. in.). This pressure bears equally on the whole surface of the whale and compresses 

 the internal organs uniformly throughout. It might perhaps be thought that the lungs 

 and heart were immune from compression through the protection of the thorax, but it 

 will readily be seen that if the viscera and musculature with their attendant blood vessels 

 were compressed and the heart, lungs, and great veins not compressed there would 

 immediately be such a surge of blood to the latter organs as would derange all blood- 

 pressure control and engorge them so that life would be endangered. Nor is it to be 

 supposed that the blubber surrounding a Blue whale acts as a rigid or semi-rigid sheath. 

 The blubber, though hard, is flexible and is quite pliable and slack ventrally from the 

 chin to the umbilicus in the region of the ventral grooves. Thus there is less protection 

 afforded by the blubber in the thoracic region than in any other part of the body. 



Uptake of oxygen. In order to understand fully the implications of hydrostatic 

 pressure on the whale's respiration it is necessary to imagine a whale submerged and 

 staying at a depth of 100 m. for some minutes. Compression of the whole body, in- 

 cluding the thorax, results, and with it the air in the lungs also becomes compressed 

 ten times. The effect of this compression on the oxygen uptake will be to raise the partial 

 pressure of the oxygen in the lungs, as pointed out by Ommanney (1932). The partial 

 pressure of oxygen in normal air is about 1 50 mm. of mercury. A partial pressure of 

 60 mm. is sufficient to keep the blood of most mammals above 80 per cent saturation 

 with oxygen. The whale's oxygen will be at 1500 mm. of mercury when a depth of 

 100 m. is first reached and may become ten times as depleted at that depth before in- 

 adequate oxygenation of the blood takes place. The oxygen in the lungs would be at a 

 partial pressure of only 6 mm. of mercury when the whale returned to the surface. In 

 other words the whale is able to make the fullest use of the oxygen in the inspired air. 

 There is evidence to show that in animals there is great power of endurance under 

 conditions of progressive anoxaemia. Experiments on dogs (C. W. and C. H. Greene, 

 1922) show extraordinary endurance, provided the blood pressure and minute volume 

 are maintained. 



Ommanney (1932), in discussing this matter, has reached the conclusion that whales 

 do not descend much deeper than 130 ft., but this estimate would appear to be too low 

 even for normal dives, and, though satisfactory evidence is lacking, it appears most 

 probable that when harpooned they can reach still greater depths. Ommanney thinks 

 that whales could not reach a depth of 600 m. because at this depth the hydrostatic 

 pressure, 60 atmospheres, would raise the partial pressure of the oxygen in the lungs 

 to 4 atmospheres and remarks that this has been found by Paul Bert to be toxic in certain 

 animals. Oxygen in the lungs would, however, be toxic at that pressure only if there 

 were an unlimited supply, whereas it will be seen from the figures of blood volume and 

 vital capacity above that one lungful of air (say 7000 1.), containing approximately 

 1400 1. of oxygen, would serve to supply the blood (8000 1.) with 17 vol. per cent 

 oxygen, which is somewhat below the normal oxygen capacity of human blood but 

 considerably above that of whales, as will be shown later. And, even if it were supposed 



